Recently, techniques for detecting chemical substances in minute quantities have been developed to detect chemical substances of minute quantities in liquids or gases, or to detect interaction between particulates contained in medium with high sensitivities. Known as such techniques for detecting chemical substances in minute quantities are, for example, Quartz Crystal Microbalance (hereinafter, just referred to as “QCM method”) and Surface Plasmon Resonance (hereinafter, just referred to as “SPR method”).
The QCM method, in which utilizing microbalance law is applied, is an art for detecting chemical substances or biosubstance by using a quarts crystal oscillator. The QCM method performs quantitative analysis by exposing surfaces of working electrodes of the crystal quartz oscillator to a sample gas or sample solution, and detecting adsorption and desorption of components of the sample to or from the surfaces of the working electrodes by monitoring a change in oscillation frequency of the quarts crystal oscillator.
More specifically, an crystal quartz oscillator 100 includes a thin crystal plate 101, and metal electrodes 102 vapor-deposited on a surface and a reverse surface of the thin crystal plate 101, as illustrated in FIG. 7. When a chemical substance or biomolecule attaches to the metal electrode 102, oscillation frequency is changed proportionally with a weight of a chemical substance or biomolecule attached thereto. That is, when a film of a sample component is formed on the surface of the metal electrode 102 of the quartz crystal oscillator 100 or a substance is adsorbed on the surface of the metal electrode 102 of the quartz crystal oscillator 100, the frequency is shifted according to how much the substance is present on the surface of the metal electrode 102 by weight per unit surface. The frequency shift phenomenon can be an indictor for detecting a chemical substance or biomolecule in a minute quantity in a medium.
A chemical sensor using the QCM method promises stable detection sensitivity because the frequency of the quartz crystal is stable over a wide temperature range. If conditions permit, such a chemical sensor can perform real-time detection of adsorbed substance in 1 to 10 ng (see Patent Citation 1, for example).
Meanwhile, the SPR method is a technique for optically detecting a chemical substance in a minute quantity. More specifically, the SPR method irradiates light on a metal thin film and monitors reflection light therefrom. When a chemical substance attaches on the metal thin film, refractive index of the metal thin film is changed. The SPR method monitors this change thereby to detect the chemical substance in a minute quantity. Chemical sensors using the SPR method have been used in the field of biotechnology, environment, and industry, in order to analyze interactions between biomolecules immobilized on the surface, to monitor antigen-antibody reactions, and to monitor sugar content, for example (see Patent Citation 2, for example).
[Patent Citation 1]
Japanese Patent Application Publication, Tokukai, No. 2001-153777 (published on Jun. 8, 2001)
[Patent Citation 2]
Japanese Patent Application Publication, Tokukai, No. 2004-163259 (published on Jun. 10, 2004)